The present invention generally relates to a traction device for attachment to the underside of a sport shoe. More particularly, this invention relates to a detachable, non-metal spike for a golf shoe, which includes a substantially non-penetrating, ground-engaging surface for providing increased traction and durability.
Spikes for golf shoes have long been used to provide traction in dirt and grass. These spikes have typically been made of metal. Traditional golf spikes have included a single metal spike, 6 to 8 mm in length. At this length, the spike penetrates the grass and passes into the roots and soil, providing a localized, essentially point, mechanical interlock, between the shoe and the sod. While this approach generates substantial traction, it also results in soil compaction and turf damage that degrades the quality of golf greens and increases their maintenance costs. In addition to turf damage, metal spikes also degrade golf carts, bridges, steps, tile floors, asphalt walkways, and clubhouse carpeting. Also, metal spikes that become loosened and fall from shoes during play damage mower blades.
Recently, golf courses have begun to prohibit the use of these traditional golf spikes due to the damage they cause to the turf, particularly to golf course greens. Starting in 1991, several courses in western states required golfers to wear spikeless athletic shoes during winter golf rounds. Within a few years, several prestigious courses followed suit and banned metal spikes. The revolution in non-metal spikes was underway with such momentum that metal spikes might be completely eliminated by 2001. Estimates by the National Golf Federation show that at the end of the 1998 golf season, one-third of the nation""s 16,000 public and private courses had gone spikeless and many of the others strongly discouraged the use of metal spikes. In a resounding vote against metal spikes, currently 80 of Golf Digest""s Top 100 courses are now spikeless.
One alternative to metal spikes features a shoe with a tread-like sole for traction, which is intended to replace the need for removable spikes. However, once the tread becomes worn, the shoe is no longer capable of providing adequate traction. The golfer must either purchase a new pair of shoes or find some way to resole the shoes with a comparable tread design.
As a compromise between metal spikes and spikeless shoes, an alternative polymer-based spike was developed that could be quickly inserted into the standard threaded holes of golf shoes. For example, one of the alternative designs replaced the single, long metal spike, or monospike, with a series of non-penetrating ridges for traction, which were formed in a fan-like design extending outwardly from the center of the spike.
The alternative spikes have several advantages. Even after dozens of rounds, the surfaces of golf course greens remain smooth, devoid of the metal spike marks that interfere with the accuracy of putts. While surface damage is virtually eliminated, subsurface root damage and soil compaction are also eliminated. In addition, less damage is inflicted on carpet, asphalt, and golf carts. Furthermore, the polymer-based spikes are lighter in weight and more comfortable than metal spikes, placing less strain on the user""s feet, ankles, knees, hips, and back.
The use of non-metal spikes, however, has not been without problems. While green damage is reduced, the generally softer, polymer-based alternative spikes wear much more rapidly than metal spikes, requiring frequent replacement throughout the season. The alternative spikes can also loosen during use. In addition, the traction provided by many of the non-metal spikes currently on the market is inferior to metal spikes. For example, some current spike designs include a circular series of small protrusions approximately 2 mm in length around the perimeter of the base of the spike. This design provides little ground-engaging ability, particularly on wet surfaces. These spikes fail to develop sufficient torque and friction between the shoe and the turf, resulting in less traction.
Traditional metal spikes achieve traction through their single, long spike penetrating the ground, which prevents lateral shifting of the feet, particularly while swinging a golf club. The highly localized, near point loading provided by monospikes resembles a bolted mechanical joint in that the stresses are concentrated at the point of load application. These stress concentrations cause damage to the adjacent material, limiting the strength of the fastening and holding capabilities. For example, two wooden boards fastened together by a nail would be damaged as a shearing force attempts to tear the nail out of the wood. In the case of monospikes, the stresses are concentrated on, and cause damage to, the turf adjacent the spike.
Improved joint strengths can be achieved by spreading these stresses out over a larger area than a single point, providing more uniform loading. For example, the two boards described above could be fastened together by applying a glue or adhesive over an area between the boards, thereby forming an adhesive joint rather than a bolted mechanical joint. In the case of golf spikes, more uniform loading may be achieved by constraining the blades of grass over a larger region.
Alternative spikes invoke a different mechanism than do monospikes to secure traction. A non-penetrating spike cannot rely upon a puncture point loaded attachment, but instead, must rely on the adhesive or gripping qualities of the spike""s surface for traction. Rather than penetrating the grass layer and digging into the soil beneath, low turf damage spikes grip the grass itself and transmit shear tractions through it, using the roots to attach to the earth beneath.
Current replaceable, non-penetrating spikes are not designed for optimal adherance to a grass surface. Adhesion is primarily created when spikes grip blades of grass. However, most non-penetrating golf spikes are not designed to grasp and hold onto grass blades. For example, one popular design uses a spiral geometry in an attempt to create adhesion. The design is apparently intended to allow for release when the golfer pivots during a drive. However, the design also allows for release during other foot movements, thereby reducing traction.
Thus, improvements in spikes for sports shoes, particularly golf shoes, are still being sought. What is needed is a replaceable spike that is less injurious to turf, especially golf course greens, and provides traction on dry and wet surfaces that is equal, or nearly equal, to that of the conventional 6 mm steel spike. Also, the spike should be lightweight and comfortable, and capable of enduring at least one season of play before replacement becomes necessary. Additional requirements include compatibility with standard threaded joints of existing golf shoes so that the low turf damage spikes can easily substitute for the traditional metal spikes, and means for attaching the new spikes that resists loosening of the spikes.
The present invention overcomes the shortcomings of known sport shoe spikes by providing a non-metal spike with enhanced durability and traction on wet and dry surfaces, without damaging turf such as golf course greens.
Using a concurrent engineering approach involving integrated design, material selection, and process development, a technically successful design and manufacturing process for the alternative, polymer-based spike of the present invention has been developed. A combination of experience-based prototypes, rapid prototyping (by solid freeform fabrication), and virtual prototypes were used to establish the design concept, design details, and process details. Success in implementing the concurrent engineering approach was aided by extensive discussions with golfers to gain a fundamental understanding of the problems with existing spikes, and to translate the problems into a coherent set of product requirements.
In one embodiment of the present invention, the spike is preferably formed as an integral, unitary body comprising a disc, cylindrical threaded post, and series of protrusions or nubs. The disc has a top and a bottom. The threaded post protrudes axially from the center of the top of the disc, which is threadedly received within an internally threaded socket on the sole of the sport shoe. The bottom of the disc engages a supporting surface such as turf, and has a plurality of spaced nubs extending outwardly from the bottom of the disc to provide traction between the shoe and the turf.
A large number of nubs, preferably more than about thirty, cover the bottom of the disc. The nubs, dispersed uniformly across the bottom of the disc, are present in a variety of heights and widths. The sizes, heights, and arrangement of the nubs are such that penetration of the soil is substantially eliminated. The large number of nubs increases the contact area, and thus friction, with the ground surface. The nubs provide traction with the turf by gripping blades of grass in the areas between the nubs and the shoe sole, providing a mechanical interlocking traction mechanism.
The design of the nubs is based on a fractal geometry design concept, with traction-generating nubs and other surface relief features repeating on successively smaller-size scales. The design concept is derived from research indicating that resistance to slipping (i.e., traction) between the fibers and matrix in composite materials is optimal when fiber surface roughness is introduced on many different size scales.
Beginning with an array of widely spaced large spikes, a succession of smaller-sized spikes arrayed between the large spikes continues to constrain grass blades when the spike engages turf. A filled polymer material composition supplies texture to the surface of the spike at the smallest scales, providing a friction coefficient contribution to the mechanical interlocking traction mechanism. The result of the fractal-based approach, combined with the large number of nubs, produces a system that approximates a continuous, adhesive-like attachment of the spike to the turf, rather than the localized, destructive loading mode of conventional metal spikes.
Besides traction and durability, another concern in the golf spike industry is ensuring the spikes are securely fastened to the shoe. Current designs use an oversized threaded polymer post to keep the spike from unscrewing. Oversized posts make insertion difficult due to increased friction. The present invention solves this problem by providing a locking mechanism with a tapered screw that is inserted into a central hole in the threaded post, thereby clamping the post to the inside of the threaded socket of the shoe sole.
Extensive tests and field trials indicate that the spikes of the present invention offer enhanced wear resistance, ease of attachment, greater initial non-penetrating traction on a variety of wet and dry grasses, and greater retained traction, even after significant wear.
From the foregoing, it will be apparent to the reader that a primary object of the present invention is to provide a spike for sport shoes that will create substantial frictional engagement between the shoe and a ground or supporting surface.
A more specific object of the invention is to provide a spike for golf shoes that provides traction between the spike and turf that is substantially similar to that of conventional metal spikes.
Another object of the present invention is to provide such a spike that is capable of uniformly distributing shear forces over a wider area of the spike disc bottom.
Another object of the present invention is to provide such a spike that is less injurious to turf.
Another object of the present invention is to provide such a spike that has an increased usable life.
Another object of the present invention is to provide such a spike that is lightweight and comfortable for the wearer.
A further object of the present invention is to provide such a spike that is replaceable and compatible with standard threaded sockets on golf shoe soles.
Still another object of the present invention is to provide an improved means of attaching the spike to the shoe sole to prevent loosening of the spike.